Base: Lockscreen blur [1/2]

Show the content behind lockscreen, blurred.

Settings: https://gerrit.omnirom.org/#/c/4702/

Change-Id: I0d7ee20d6b415567f0051d716ba0db2e55511e91
Also hide "emergency only" label if signal bars are hidden by option

Change-Id: Iad3f93bad0b4dc920dcd558ad236460111b6a8c9